Observability Metrics Support for GraphQL

[ThisaruGuruge]

Description:

Part of ballerina-platform/ballerina-lang#42562

Similar to other GraphQL dashboards, we should include the following metrics:

1. No. of requests
2. Requests per second
3. Request error rate
4. Errors per second
5. Response latency
6. Top 10 most requested operations
7. Top 10 slowest operations
8. Top 10 operations that errored
9. Top 10 fields requested
10. No. of Query, Mutation, and Subscription operations
11. CPU usage
12. Memory usage

The HTTP service can obtain above 1, 2, 11, and 12.

Others have to be published from the GraphQL Engine.

As the first step, we can consider the 1, 2, 3, 4, 5, 6, and 10. We can also consider 9 for the first phase, but we can keep it for the second phase with the rest of the metrics.